The present invention relates to an apparatus for controlling the opening and closing operations of a throttle valve, which is used for controlling the amount of intake air taken into an internal combustion engine, and to a vehicle internal combustion engine using the apparatus.
The output power of a vehicle engine is usually controlled by opening and closing a throttle valve which is responsive to movements of an acceleration pedal operated by a driver. The throttle valve is placed in an air intake path of the engine and is used for controlling the output power of the engine by adjusting the amount of intake air.
A throttle valve opening and closing apparatus is disclosed in JP-A-150449/1988. This apparatus includes a control unit for determining the opening degree of a throttle valve in response to a command value for a desired amount of acceleration, a motor for driving the throttle valve to set its opening degree to a value between a fully closed position and a fully opened position, a return spring for pushing the throttle valve in the valve closing direction, and an elastic member for pulling the throttle valve in the valve opening direction.
The valve pushing force of the return spring is set to be lower than the valve pulling force of the elastic member, and the motor driving force to close the throttle valve is set to be smaller than the valve pulling force of the elastic member. Thus, when the motor does not drive the throttle valve, the throttle valve is pushed by the return spring in the closing direction, and the position of the throttle valve is automatically adjusted to an equilibrium position established by the pushing force of the return spring and the pulling force of the elastic member. In this way, an opening degree at an adjusted position of the throttle valve is predetermined so as to secure a minimal amount of intake air sufficient to start the engine at a low temperature, and to make it possible to drive the vehicle, even if the driving force of the motor can not be generated.
Furthermore, a throttle valve opening and closing apparatus for adjusting the rotation speed during idling operation of an internal combustion engine is disclosed in U.S. Pat. No. 4,991,552. In this apparatus, a first lever mechanism and a second lever mechanism are provided, and a driving force is applied to the shaft of a throttle valve in the opening direction.
The first lever mechanism is driven by an electrical motor or an air actuator and is used for adjusting the rotation speed during idling operation. Thus, the first lever mechanism is composed so as to cause the throttle valve to open by about 25 deg. from the fully closed position. Conversely, the second lever mechanism opens and closes the throttle valve in response to en acceleration pedal operation performed by a driver, and the operation performed by the first lever mechanism takes priority over the valve opening operation performed by the second lever mechanism.
Moreover, the first and second lever mechanisms apply a force to the throttle valve only in the opening direction, and the force in the closing direction is applied by a return spring.
In a present day vehicle, the target output power is generated by controlling the opening of the throttle valve to a position between a fully closed state and a fully open state. For emitting a cleaner exhaust gas and for other reasons, it is desirable to finely control the air to fuel ratio. Especially in a direct injection engine, fine control of the air to fuel ratio is desired so as to be able to use stratified combustion and uniform combustion properly and effectively. Therefore, it is necessary to control the opening of the throttle valve so as to follow the command value accurately between the fully closed and fully open states.
Furthermore, it is preferable to provide a redundant means for closing the throttle valve. By providing a redundant means, even if one of the means becomes inoperable, it is possible to quickly close the throttle valve to a predetermined position (hereafter referred to as the default position) to prevent the vehicle from running away.
In the first of the two above-mentioned conventional techniques for holding the state in which the throttle valve is slightly open at the default position, a valve pushing means and a valve pulling means for applying forces in opposite directions, that is, a return spring and an elastic member, are provided. Although it is comparatively easy to control the opening degree of the throttle valve so as to follow the command value if only one of the two above means is operated, when the other means begins to become effective, the control unit can not control the throttle valve so as to follow the output power command value quickly in response to changes in the force generated by the two means, and so the delay in responding to the command becomes large. Thus, the accuracy and response time in the control of the output power is degraded.
On the other hand, in the throttle valve opening and closing apparatus disclosed in the second one of the above-mentioned conventional techniques, the control over the opening of the throttle valve does not deal with running operations of the vehicle, but concerns only the idling operation of the engine. In this apparatus for adjusting the engine rotation speed during idling, the valve pushing force is applied to the throttle valve by one return spring, and the control unit holds the position of the throttle valve at the default position so that it is slightly open. However, since this control unit is provided to adjust the rotation speed during idling, it controls the throttle valve only in the range from the fully closed state to 25 deg. If the throttle valve is controlled in the range from the fully closed state to the fully open state (90 deg.) by using this apparatus, which has been designed for adjusting the rotation speed during idling, because of the restriction due to the oscillation range of the lever mechanisms, it is inevitable that the size of the lever mechanism will become larger, and so it will be impractical to use this apparatus in a vehicle.
Moreover, if the valve closing operation is carried out by using only the return spring, as in the latter apparatus, there is the possibility that it will become impossible to close the throttle valve if the return spring becomes broken. Furthermore, if a quick closing operation of the throttle valve is needed, since the throttle valve is driven by only the return spring, the response time is large, and the throttle valve cannot possibly be closed within the necessary time (see FIG. 11). If a large return spring force is used, the load force needed in opening the throttle valve increases, and the valve opening operation is delayed. To solve this problem of the delay in the valve opening operation, it is necessary to increase the size of the throttle valve driving means (if a motor is used, the size of the motor would need to be increased).